Transient intermediate structures between reactants and products in chemical reactions—transition states—can be probed by colliding the reactants at a well-defined collision energy E_col, and then observing the product scattering angle θ and product kinetic and internal energy. By varying E_col, sharp variations, or resonances, can be observed in the probability of forming the product at a particular scattering angle and internal energy. These resonances correspond to the energy-level structure of the transition state and have been investigated in the F + HD → HF + D reaction for decades (1). On page 936 of this issue, Chen et al. (2), through scattering experiments with high resolution and sensitivity, have observed a distinct set of scattering resonances for F + H, which theory can only reproduce by including electronic spin and orbital angular momentum. Thus, the authors measure the transition-state structure with previously unattainable sensitivity.

在化学反应中反应物和产物之间的过渡中间结构（过渡态）可以通过以明确定义的碰撞能E _col碰撞反应物，然后观察产物散射角θ以及产物动能和内能来探测。通过改变E _col，可以观察到以特定散射角和内能形成产物的可能性的急剧变化或共振。这些共振对应于过渡态的能级结构，并且已经在F + HD→HF + D反应中进行了数十年的研究（1）。在本期杂志的第936页上，Chen等人。（2），通过高分辨率和高灵敏度的散射实验，观察到了F + H的一组独特的散射共振，该理论只能通过包含电子自旋和轨道角动量来重现。因此，作者们以以前无法达到的灵敏度来测量过渡态结构。